The invention relates to an apparatus for activating and/or deactivating a security device, particularly an entry device for a motor vehicle, having a portable transmitter unit for wirelessly transmitting a coded information item which is received by a receiver apparatus and is compared with a prescribed coded information item, the receiver apparatus being capable of outputting an actuation signal to the security device if the two information items match and the receiver apparatus being connected to a mechanical device for operating the security device.
Known apparatuses for activating and/or deactivating a locking system in a motor vehicle have a portable transmitter which, on request, transmits a coded information item to a receiver device which is permanently installed in the motor vehicle. The receiver device compares the transmitted coded information item with a prescribed information item which is generated in it. If the two information items match, the locking system is actuated by the receiver device.
So that it is still possible to operate the security device when the battery in the transmitter fails, for example, the receiver device is connected to a lock cylinder which can be operated mechanically using a key, which likewise activates or deactivates the security device.
Since, normally, only the remote control is used to actuate the locking system, it is necessary to ensure that only quite specific transmitters are able to unlock or lock a central locking system. The transmission protocols are therefore provided with a fixed allocation comprising a fixed code and an alternating code.
To calculate the respective next alternating code values, the same algorithm is used in the transmitter and in the receiver. In this context, the receiver has a so-called capture range for unlocking and locking, said capture range always permitting a plurality of future coded information items as being valid. The alternating code is changed in the transmitter by request; in the receiver, on the other hand, it is equated to that of the transmitter when a valid information item is received. Hence, if a plurality of coded information items from the transmitter do not reach the receiver, a permissible coded information item may be outside the capture range of the receiver and may thus not be recognized by the receiver.
Particularly when radio remote controls are used, where coded information items are transported over long ranges using a radio signal, interference within the transmission link may impair or completely interrupt the receiver""s reception of the coded information item transmitted by the transmitter. Such interference can also be produced deliberately in order to record the coded information items transmitted by the transmitter and use them to open the motor vehicle without authorization. Reliable operation of the security device is therefore not ensured.
The invention is thus based on the object of specifying an apparatus for activating and/or deactivating a security device in which unauthorized deactivation of the security device is reliably prevented.
The invention achieves the object by the feature that the receiver apparatus is disabled for the reception and/or evaluation of the coded information item and/or for the output of the actuation signal to the security device after the security device has been mechanically activated, the block being lifted after the security device has been mechanically deactivated.
The invention has the advantage that blocking the receiver prevents coded information items transmitted by the transmitter from being used to open the security device without authorization. After the transmitter has been operated a plurality of times, the user will realize that the receiver is not reacting to the transmitter signals being transmitted, and the desired action cannot be carried out. To carry out the action anyway, he will chose the conventional procedure, i.e. inserting a key into the lock cylinder and unlocking or locking the security device. However, since the radio remote control is put out of operation at the same time as this mechanical locking, this also reliably prevents tapped coded information items which have not yet been registered by the receiver from being able to be used to deactivate the security device. Only after mechanical deactivation of the security device does the radio remote control work in the customary manner again.
A coded information item transmitted from the transmitter to the receiver directly after the security device has been mechanically deactivated is used to shift all coded information items, possibly recorded beforehand, to the realms of the past, since the receiver, having received a valid information item from the transmitter, equates said information item to the one which is present in the receiver. This means that they are outside the capture range of the receiver, so that no actions can be triggered using these tapped coded information items.
This takes place particularly quickly and reliably if the receiver apparatus, having established that the security device has been mechanically deactivated, sends a stimulus signal to the portable transmitter unit for transmission of the coded information item.
Advantageously, the portable transmitter unit and the receiver apparatus each contain a code generator, the first code generator in the portable transmitter unit generating the coded information item which is to be transmitted, and the second code generator in the receiver apparatus generating the prescribed coded information item, both code generators operating on the basis of the same algorithm.
In this context, one or more respective random numbers which are independent of one another may be used as code, said random numbers being processed and compared with one another in the receiver on the basis of particular arithmetic rules.
In one development, the code generators in the portable transmitter unit and in the receiver apparatus advance the algorithm automatically. In this context, an algorithm can be used to modify the coded information item which is to be transmitted and the prescribed coded information item a plurality of times. It is also conceivable, however, for the algorithm to be changed after each action in the portable transmitter unit in order to modify the coded information item which is to be transmitted and the prescribed coded information item.
The system""s security against tapping is increased further as a result of the code generator in the portable transmitter unit being advanced after transmission of the coded information item has ended and the code generator in the receiver apparatus being advanced after reception of a valid coded information item.
To prevent the capture range of the receiver apparatus from being exceeded by the coded information item in the portable transmitter unit after a particular time, the code generator in the portable transmitter unit and the code generator in the receiver apparatus are advanced by the same number of steps.